Carrier and microstructure tuning for improving the thermoelectric properties of Ag8SnSe6 via introducing SnBr2

Abstract

Abstract The argyrodite compounds (A (12−n) m/m+ B n+X 6 2− (A m+ = Li+, Cu+, and Ag+; B n+ = Ga3+, Si4+, Ge4+, Sn4+, P5+, and As5+; and X2− = S2−, Se2−, or Te2−)) have attracted great attention as excellent thermoelectric (TE) materials due to their extremely low lattice thermal conductivity Among them, Ag8SnSe6-based TE materials have high potential for TE applications. However, the pristine Ag8SnSe6 materials have low carrier concentration (< 1017 cm−3), resulting in low power factors. In this study, a hydrothermal method was used to synthesize Ag8SnSe6 with high purity, and the introduction of SnBr2 into the pristine Ag8SnSe6 powders has been used to simultaneously increase the power factor and decrease the thermal conductivity (κ). On the one hand, a portion of the Br− ions acted as electrons to increase the carrier concentration, increasing the power factor to a value of ∼698 µW·m−1·K−2 at 736 K. On the other hand, some of the dislocations and nanoprecipitates (SnBr2) were generated, resulting in a decrease of κ 1 (−0.13 W·m−1·K−1) at 578 K. As a result, the zT value reaches ∼1.42 at 735 K for the sample Ag8Sn1.03Se5.94Br0.06, nearly 30% enhancement in contrast with that of the pristine sample (−1.09). The strategy of synergistic manipulation of carrier concentration and microstructure by introducing halogen compounds could be applied to the argyrodite compounds to improve the TE properties.

Keywords

• Ag8SnSe6
• thermoelectric (TE) performance
• lattice thermal conductivity
• SnBr2 introduction
• hydrothermal method